Cross-tolerance between orphanin FQ and morphine in rats / 第二军医大学学报

ABSTRACT

Objective:To assess whether intrathecal orphanin FQ can develop the antinociceptive effect tolerance,and whether there is a cross tolerance between the antinociceptive effect of intrathecal orphanin FQ and the ? opioid receptor agonist morphine.Methods: Tail flick test was used to observe the change of antinociceptive effect after orphanin FQ/morphine intrathecal microinjection into the rats tolerant to acute or chronic morphine/orphanin FQ.Results:Like morphine,large dosage of continuous intrathecal orphanin FQ microinjection produced tolerance to the antinociceptive effect,but there was no apparent cross tolerance between the orphanin FQ and morphine; Hyperalgesic response was found in morphine tolerant rats,but not in orphanin FQ tolerant rats.Conclusion:Lack of cross tolerance between the antinociceptive effect of intrathecal orphanin FQ and morphine indicates that the mechanism of tolerance to orphanin FQ may differ from that to morphine; The antinociceptive effect of intrathecal orphanin FQ may be largely related with its specific receptor in the spinal cord.